SilversideAtherinidae

The fish under the jetty light is a close relative of the guppy. Silversides sit in Atherinomorpha, the branch that also holds the killifishes and guppies of fresh water and the halfbeaks, needlefishes and flying fishes of the open sea. It is a lineage of the top of the water: small animals living in the first meter of it, feeding at the surface film, eaten from above and below at the same time.

The body is assembled to match. Two small dorsal fins set far apart and well back, a small mouth, a nearly transparent body carrying one silvered stripe along each side, and no lateral line worth the name. That last one is worth stopping on. The lateral line is the pressure sense most schooling fish use to hold station on their neighbors, and this family has either lost it or reduced it to almost nothing, which leaves eyesight to do the work. The school is a visual structure, and darkness takes it apart. What the school does when it is working, and why a light after dark is where you go to watch one, are on the species pages.

The eggs are the family signature. An atherinomorph egg comes with long sticky threads growing off its envelope, so instead of joining the plankton it catches on weed, root, rope or netting and stays where it was laid. The American relatives push this as far as it goes: the grunion rides a night tide up a 🇺🇸 California beach, spawns in wet sand above the water line and leaves on the next wave.

Four are listed here. One of them occurs naturally in this sea and nowhere else and has nonetheless spread along much of the eastern Mediterranean, which the species pages take apart.